Stabilization procedure and apparatus for polymeric fibrous materials

ABSTRACT

An improved continuous process and apparatus are provided for the uniform stabilization of a strand of polymeric fibrous material which is capable of undergoing thermal stabilization. The strand is continuously wound in a plurality of turns and continuously unwound from at least one rotating roll having a porous surface while a gas at an elevated temperature is expelled outwardly through the surface of the porous roll and penetrates the fibrous configuration of the strand wound upon the roll. In a preferred apparatus in accordance with the present invention the porous roll situated within a heat treatment chamber is internally provided with a plurality of individually adjustable heating elements along its length. The resulting stabilized material retains its original fibrous configuration essentially intact, exhibits enhanced thermal stability, and is capable of undergoing carbonization. In a particularly preferred embodiment of the invention the precursor is an acrylonitrile homopolymer and air having a temperature of at least about 260* C. is expelled through the surface of the rotating porous roll.

Matted States Patent [72] Inventor Dagobert E. Stuetz Westfield, NJ.

[21] Appl. No. 865,334

[22] Filed Oct. 10, 1969 [45] Patented Jan.4, 1972 [73] AssigneeCelanese Corporation New York, N.Y.

[54] STABILIZATION PROCEDURE AND APPARATUS FOR POLYMERIC FIBROUSMATERIALS 11 Claims, 3 Drawing Figs.

[51] Int. Cl F27b 9/28, F26b 13/08 [50] Field of Search 263/3, 6 C;34/155, 160

[5 6] References Cited UNITED STATES PATENTS 2,701,765 2/1955 Codichiniet al 263/3 3,161,484 12/1964 Bagnoli et al. 34/155 X 3,387,833 6/1968Whittaker et al.

Pn'mary Examiner-John J. Camby Attorneys-Thomas J. Morgan, Charles B.Harris and Kenneth E. Macklin ABSTRACT: An improved continuous processand apparatus are provided for the uniform stabilization of a strand ofpolymeric fibrous material which is capable of undergoing thermalstabilization. The strand is continuously wound in a plurality of turnsand continuously unwound from at least one rotating roll having a poroussurface while a gas at an elevated temperature is expelled outwardlythrough the surface of the porous roll and penetrates the fibrousconfiguration of the strand wound upon the roll. In a preferredapparatus in accordance with the present invention the porous rollsituated within a heat treatment chamber is internally provided with aplurality of individually adjustable heating elements along its length.The resulting stabilized material retains its original fibrousconfiguration essentially intact, exhibits enhanced thermal stability,and is capable of undergoing carbonization. In a particularly preferredembodiment of the invention the precursor is an acrylonitrilehomopolymer and air having a temperature of at least about 260 isexpelled through the surface of the rotating porous roll.

mcmenm 41912 31632092 SHEET 1 BF 2 memmm m 3632.092

SHEET 2 OF 2 STABILIZATION PROCEDURE AND APPARATUS FOR POLYMERIC FIBROUSMATERIALS BACKGROUND OF THE INVENTION In the past procedures have beenproposed for the conversion of organic polymeric fibers to a modifiedform possessing enhanced thermal stability. Such modification hasgenerally been accomplished by heating the fibrous material in anappropriate atmosphere at moderate temperatures for extended periods oftime. The product may be suitable for use as an intermediate in theformation of carbonized fibrous materials, or for direct utilization inapplications where fibers of enhanced thermal stability are required.

U.S. Pat. No. 2,913,802 to Barnett and U.S. Pat. No. 3,285,696 toTsunoda disclose representative processes for the conversion of fibersof acrylonitrile homopolymers of copolymers to a heat resistant formwherein the fibers are heated in an oxygen-containing atmosphere. Suchprior art stabilization techniques have commonly been directed to batchoperations which require relatively long heating periods.

The more recent Belgian Pat. No. 700,655 discloses a procedure whereby acontinuous length of an acrylonitrile copolymer may be continuouslysubjected to a stabilization treatment to produce essentially completeoxygen saturation while maintained in air at a temperature not exceeding250 C., e.g., three hours or more at 220 C. Commonly assigned U.S, Ser.No. 749,957, filed Aug. 5, 1968 of Dagobert E. Stuetz additionallydiscloses an improved generically defined process wherein certainacrylic fibrous precursors surprisingly may be continuously stabilizedat more highly elevated temperatures than previously deemed possible.

I-Ieretofore a common technique for the continuous stabilization of acontinuous length of fibrous material has involved the passage of alength of the material through the interior of a tubular muffle furnaceprovided with an appropriate atmosphere. Rollers have commonly beensituated at each end of the furnace to direct movement of the strand sothat it is aligned along the axial center of the furnace. The residencetime achieved within such a heat treatment zone is by necessitydetermined by the length of the furnace and by the strand speed. Inorder to achieve a commercially acceptable production level the oven (1must be extremely long in order to make possible a relatively highstrand speed, or (2) the strand must be returned for a multiplicity ofpasses. When using such an arrangement, the stringing of the apparatusprior to carrying out the process is often tedious and time consuming.

In continuous preoxidation systems of the prior art in which the strandbeing treated is wound upon a pair of spaced converging rolls and heatedair is supplied to the same from an external source, it has beenessential to provide a plurality of ovens in series if the strand is tobe subjected to a plurality of successively elevated temperatures. Also,an appreciable time lapse may be required for the oven to attain theoperating temperature desired.

When stabilization of a strand of polymeric fibrous material isconducted in accordance with the teaching of US. Ser. No. 865,333, filedOct. 10, 1969, in the name of William M. Cooper, by contact with thesurface of a rotating heated roll having an internal heat source and agas impervious surface, the stabilization reaction has a tendency to beat least initially concentrated upon he side of the fibrous strand wheredirect physical contact is made with the heated roll.

It is an object of the invention to provide an efficient continuousprocess and apparatus for the stabilization of a strand of polymericfibrous material in which the strand undergoes stabilization on a highlyuniform basis.

It is an object of the invention to provide an improved stabilizationapparatus capable of accomplishing the continuous stabilization of astrand of a polymeric fibrous material while accommodating a relativelylarge precursor inventory per unit of area.

It is an object of the invention to provide an efficient process for thepreoxidation of an acrylic yarn to render the same capable of undergoingcarbonization.

It is another object of the invention to provide a compact stabilizationapparatus capable of penetrating a fibrous strand with a hot gas atsuccessively elevated temperatures as the strand travels along thesurface of a porous roll.

These and other objects, as well as the scope, nature, and utilizationof the invention will be apparent from the following detaileddescription and appended claims.

SUMMARY OF THE INVENTION It has been found that a process for thestabilization of a strand of polymeric fibrous material capable ofundergoing thermal stabilization comprises passing the strand through aheat treatment zone wherein the strand is continuously wound in aplurality of turns and continuously unwound from at least one rotatingroll having a porous surface while a gas at an elevated temperature isexpelled outwardly through the surface of the porous roll and penetratesthe fibrous configuration of the strand wound upon the roll, andcontinuously withdrawing the resulting stabilized strand of fibrousmaterial from the heat treatment zone which retains its original fibrousconfiguration essentially intact, exhibits enhanced thermal stability,and is capable of undergoing carbonization.

An apparatus for the continuous stabilization of a strand of polymericfibrous material comprises a substantially enclosed heat treatmentchamber, means for continuously introducing a strand of fibrous materialinto the heat treatment chamber, means for continuously withdrawing astrand of fibrous material from the heat treatment chamber, at least onerotatable roll situated within the chamber having a porous surface,drive means capable of rotating the roll, conduit means essentiallycoextensive with the length of the roll in a communicative relationshipto the porous surface of the roll, heating means situated within therotatable roll, and means for supplying a gas to the conduit means.DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view partially cutaway of a preferred apparatus of the present invention showing thepositioning of a strand of polymeric fibrous material upon a rotatabletapered driven roll having a porous surface while a gas at an elevatedtemperature is expelled outwardly through the surface of the porous rolland penetrates the fibrous configuration to the strand of producestabilization.

FIG. 2 is a cross section of the tapered porous roll shown in theapparatus of FIG. 1.

FIG. 3 is a perspective view of a portion of an alternative apparatusarrangement in which the strand undergoing treatment is continuouslywound in a plurality of turns and continuously unwound from a rotatableporous roll having an essentially cylindrical configuration as well asupon a rotatable skewed roll in a paired spaced relationship to theporous roll.

DETAILED DESCRIPTION OF THE INVENTION The stabilized materials formed inaccordance with the present invention retain the original fibrousconfiguration of the organic polymeric precursor, possess an enhancedthermal stability, and are capable of undergoing carbonization byheating in a nonoxidizing atmosphere according to procedures known inthe art, e.g., heating in a nitrogen atmosphere at l,000 C. Thestabilized strands formed in the present process may alternatively beused as heat-resistant fibrous insulative materials, or in otherapplications where a thermally stable fibrous material is required.Additionally, the fibrous materials when derived from an acrylicprecursor are nonbuming when subjected to an ordinary match flame andfind utility in the formation of flame-resistant fabrics.

The organic polymeric materials which are treated in accordance with thepresent invention may be of varied composition. Those precursors whichare capable of undergoing thermal stabilization may be selected. Forinstance, the organic polymeric precursor may be an acrylic polymer, acellulosic polymer, a polyamide, a polybenzimidazole, polyvinyl alcohol,etc. As discussed hereafter, acrylic polymeric materials areparticularly suited for use in the present process. illustrativeexamples of suitable cellulosic materials include the natural andregenerated forms of cellulose, e.g., rayon. illustrative examples ofpolyamide precursors include the aromatic polyamldes such as nylon 6Twhich is formed by the condensation of rhexamethylenediamine andterephthalic acid. An illustrative example of a suitablepolybenzimidazole is poly-2,2-mphenylene-S ,5 '-bibenzimidazole.

The acrylic polymer selected for use as the precursor may be formedprimarily of recurring acrylonitrile units. For instance, the acrylicpolymer should generally contain not less than about 85 mol percent ofrecurring acrylonitrile units with not more than about l mol percent ofa monovinyl compound which is copolymerizable with acrylonitrile such asstyrene, methyl acrylate, methyl methacrylate, vinyl acetate, vinylchloride, vinylidene chloride, vinyl pyridine and the like, or aplurality of such monomers.

In a preferred embodiment of the invention the starting material isselected in accordance with the teachings of US. Ser. No. 749,957, filedAug. 5, i968, of Dagobert E. Stuetz, which is assigned to the sameassignee as the instant invention, and is herein incorporated byreference. More specifically, the copolymer should contain no more thanabout 5 mol percent of one or more monovinyl comonomers copolymerizedwith acrylonitrile. In a particularly preferred embodiment of theinvention the acrylic polymer is an acrylonitrile homopolymer.

The strand of polymeric fibrous material which is treated in accordancewith the present invention is preferably a continuous rnultifilamentyarn which may be formed by conventional techniques. Various threads,ropes, and cables, or continuous lengths of similar fibrousconfigurations may be selected. The strand which serves as the startingmaterial may optionally be provided with a twist which tends to improveits handling characteristics. For instance, a twist of about 0.l to 5t.p.i., and preferably about 0.3 to 1.0 t.p.i. may be utilized.

The fibrous material which serves as the starting material optionallymay be highly oriented. Such orientation is generally capable ofenhancing the tensile properties of the resulting stabilized fibrousmaterial, as well as of any carbon materials derived therefrom. Anacrylic starting material may be oriented by hot drawing to a relativelyhigh single-filament tensile strength of at least about 4 grams perdenier prior to stabilization. For instance, fibrous acrylic startingmaterials which possess a single-filament tensile strength of about 4 to9 grams per denier may be selected for use in the process.

As will be apparent to those skilled in the art, the atmosphere providedin the heat treatment zone may be varied. For instance, a cellulosicprecursor is commonly stabilized in (I) an oxygen-containing atmosphereor in (2) an inert or nonoxidizing atmosphere, such as nitrogen, helium,argon, etc. Additionally, precursors such as an acrylic polymer, apolyamide, a polybenzimidazole, or polyvinyl alcohol are commonlystabilized in an oxygen-containing atmosphere. Air may be convenientlyselected as the oxygen-containing atmosphere for use in the process. Ifdesired, the precursor may be preliminarily treated with catalyticagents which are capable of promoting the stabilization reaction. Whenthe stabilization treatment is conducted in an oxygen-containingatmosphere, it is commonly termed a preoxidation" treatment particularlywhen followed by carbonization which is conducted in an inertatmosphere.

The stabilization zone is substantially enclosed in order to facilitatethe confinement and withdrawal of off gases and/or the maintenance of anappropriate atmosphere. When a nonoxidizing atmosphere is desired withinthe heat treatment chamber the strand may pass through a seal as itcontinuously enters and leaves the heat treatment chamber in order to exclude oxygen.

The stabilization of fibers of acrylonitrile homopolymers and copolymersin an oxygen-containing atmosphere involves (l)an oxidativecross-linking reaction of adjoining molecules as well as (2) acyclization reaction of pendant nitrile groups to a condenseddihydropyridine structure. While the reaction mechanism is complex andnot readily explainable it is believed that these two reactions occurconcurrently, or are to some extent competing reactions.

The cyclization reaction involving pendant nitrile groups which occursupon exposure of an acrylic fibrous material to heat is generally highlyexothermic and, if uncontrolled, results in the destruction of thefibrous configuration of the starting material. ln some instances thisexothermic reaction will occur with explosive violence and result in thefibrous material being consumed by flame. More commonly, however, thefibrous material will simply rupture, disintegrate and/or coalesce whenthe critical temperature is reached. As the quantity of comonomerpresent in an acrylonitrile copolymer is increased, a fibrous materialconsisting of the same tends to soften at a progressively lowertemperature and the possible destruction of the original fibrousconfiguration through coalescence of adjoining fibers becomes a factorof increasing importance. The critical temperature referred to herein isdefined as the temperature at which the fibrous configuration of a givensample of acrylic fibrous starting material will be destroyed in theabsence of prior stabilization.

In a preferred embodiment of the invention the acrylic starting materialexhibits a critical temperature of at least about 300 C., e.g., about300 C. to 330 C. In addition to visual observation, the detection of thecritical temperature of a given acrylic fibrous material may be aided bythe use of thermoanalytical methods, such as differential scanningcalorimeter techniques, whereby the location and magnitude of theexothermic reaction can be measured quantitatively.

The strand of polymer fibrous material is continuously wound a pluralityof turns in a single strand thickness and continuously unwound from atleast one cantilevered rotating roll having a porous surface while a gasat an elevated temperature is expelled outwardly through the surface ofthe porous roll and penetrates the fibrous configuration of the strandwound upon the roll. The roll or rolls are preferably positioned withinan essentially enclosed heat treatment chamber or zone wherebystabilization off gases may be confined and withdrawn and/or theappropriate atmosphere maintained. As the fibrous strand travels acircuitous path around the periphery of one or more porous roll it isstabilized. The porous roll may be in the configuration of (l) atruncated cone [see FIGS. 1 and 2] or (2) it may by cylindrical havingan essentially uniform diameter {see FIG. 3].

As illustrated in FIG. 1, when the porous roll has a conical or taperedconfiguration, the strand is passed onto the rotating roll surface atone end and is wound around the roll in a plurality of turns prior toleaving the porous roll surface at the other end. A strand ofsubstantial length may be continuously stabilized within a relativelysmall area. The strand is wound about the periphery of the roll in sucha manner that it is in intimate contact with the rotating porous surfaceof the roll and moves along the rotating roll in a helical or spiralpath. A heated gas is continuously expelled through the surface of theporous roll which effectively penetrates the fibrous configuration ofthe strand. If desired, a plurality of porous conical or tapered rollsmay be provided within the heat treatment zone. The rolls may beintergeared for actuation in unison according to known techniques. Thestrand may accordingly pass from the narrow end of one rotating roll tothe wide end of an adjacent rotating roll where the stabilization iscontinued. if desired, the gas may be expelled from the surfaces of aseries of rolls at successfully elevated temperatures.

in another embodiment of the invention at least one cylindrical porousrotatable driven roll 1 is provided in a paired relationship to arotatable skewed roll 2, ie an inclined roll, as illustrated in H6. 3.Alternatively, tapered roll pairs may be utilized with the taper of eachroll being in the same ratio within a given pair. The resulting pair ofrolls may be positioned in the same or a different plane. The pair ofrolls is aligned so that when rotated a fibrous strand wound or loopedabout the same will track from one end of the porous roll to the otherwhile retaining a thickness of a single strand. Preferably the porousroll is of a substantially larger diameter than the skewed roll. Theskewed roll optionally may be driven and provided with a porous surfacethrough which a gas at an elevated temperature is also expelled. If notdriven the skewed roll may idle, i.e. be rotated by the movement of thefibrous strand wound thereon. The rolls are preferably provided in asingle plane and aligned so that their axes converge slightly. As willbe apparent to those skilled in the fiber art, the strand will track thelength of the heated roll and move towards the end where the axesconverge. The lesser the degree of convergence the lesser the rate ofthe lateral movement of the strand along the length of the heated roll.

The strand is passed to each roll at an angle essentially perpendicularthereto. When a skewed roll is utilized, the strand tends to leave eachroll for passage to the roll paired therewith at an angle other than 90.If desired, the strand may be introduced into the heat treatment zonefor a plurality of passes in the event the size of the heat treatmentchamber is inadequate to complete stabilization during a single pass.

The strand is treated while in contact with one or more rotating rollhaving a porous surface while a gas at an elevated temperature isexpelled outwardly through the surface of the porous roll and penetratesthe fibrous configuration of the strand wound upon the roll as describedat least until the strand attains a stabilized form which retains itoriginal fibrous configuration essentially intact. The resultingstabilized strand is commonly black in appearance. The treatment timesduring which the strand contacts a porous roll and temperatures willvary depending upon the composition and the exact configuration of thestrand of polymeric fibrous material. Temperatures are selected whichmay be withstood by the strand without the destruction of its originalfibrous configuration, e.g., through softening, melting, an uncontrolledexothermic reaction, or decomposition. The higher the temperature of thegas expelled through the porous roll generally the greater the rate atwhich the stabilization reaction occurs. When the fibrous strand iscellulosic in nature, e.g., rayon or cellulose acetate, thestabilization treatment may commonly be conducted at about 200 to 320 C.for a porous roll contact time of about 5 to 180 minutes. When thefibrous strand is a polyamide, e.g., nylon 6T, the stabilizationtreatment may commonly be conducted at about 200 to 350 C. for a porousroll contact time of about 5 to 120 minutes. When the fibrous strand isa polybenzimidazole, e.g., poly-2,2-m-phenylene-5,5 '-bibenzimidazole,the stabilization treatment may commonly be conducted at about 400 to550 C. for a porous roll contact time of about 2 to 30 minutes. When thefibrous strand is polyvinyl alcohol, the stabilization treatment maycommonly be conducted at about 180 to 200 C. for a porous roll contacttime of several hours. More highly elevated temperatures may optionallybe utilized during the final portion of the stabilization treatment.

When the strand of polymeric fibrous material is an acrylonitrilehomopolymer or an acrylonitrile copolymer containing at least about 95mol percent of one or more monovinyl units copolymerized therewith, thestabilization temperature is preferably selected in accordance with theteachings of commonly assigned U.S. Ser. No. 749,957 of Dagobert E.Stuetz which is herein incorporated by reference. With such startingmaterials the gas expelled through the surface of the porous roll may beprovided at a temperature of about 260 C. up to about 10 C. below thecritical temperature of the starting material. The entire stabilizationtreatment may be conducted by heating the fibrous material at atemperature substantially within the above range. In a preferredembodiment of the invention a strand of an acrylonitrile homopolymerfibrous material is heated at about 260 C. to about 300 C. and at atemperature of about 270 C. to 290 C. in a particularly preferredembodiment of the invention.

The stabilization treatment of the present process may be expedited ifthe gas is expelled through the surface of one or more porous roll overwhich the strand passes at successively elevated temperatures as thestrand travels through the heat treatment chamber. For instance, the gaswhich penetrates the surface of a given porous rotating roll may besupplied to the roll surface at successively elevated temperatures alongthe length of the roll. Alternatively, a plurality of porous rolls maybe provided in series with each successive roll expelling a gas throughits surface at a more highly elevated temperature than the previous rollover which the strand passed. If desired, when stabilizing a strand ofthe preferred acrylic precursor the gas may be initially expelled at atemperature slightly below 260 C. and subsequently increased to at leastabout 260 C. where a substantial portion of the stabilization reactionoccurs. During the final portion of the stabilization reaction thecritical temperature exhibited by the unmodified starting material maycommonly be exceeded. When it is desired to produce a strand ofstabilized acrylic product which is capable of being carbonized orcarbonized and graphitized to a product of high tensile strength, thepresent continuous process optionally may be conducted on a multiplestage basis in accordance with the teaching of U.S. Ser. No. 749,959 ofMichael J. Ram, filed Aug. 5,1968, now U.S. Pat. No. 3,539,295, which isassigned to the same assignee as the instant invention, and is hereinincorporated by reference.

A strand of acrylic fibrous material is subjected to the stabilizationtreatment for a residence time sufficient to impart a bound oxygencontent of at least about 7 percent by weight. Higher bound oxygencontents, e.g., up to 15 percent or more, may be achieved upon theextended treatment. The weight percentage of bound oxygen present in thematerial may be determined by routine analytical techniques, such as theUnterzaucher analysis. When operating with a strand of acrylonitrilehomopolymer or an acrylonitrile copolymer containing at least about molpercent of recurring acrylonitrile units and up to about 5 mol percentof one or more monovinyl units copolymerized therewith at astabilization temperature of at least about 260 C., stabilizationresidence times may commonly range from about 10 minutes to aboutminutes. More extended residence times (e.g. up to 24 hours) arecommonly required when utilizing acrylonitrile copolymers containing ahigher percentage of comonomer and stabilization temperaturessubstantially below 260 C., e. g., 200 C.

When utilizing a plurality of rotating porous rolls in the heattreatment zone, it is possible to vary slightly their relative speeds ofrotation or the relative roll circumferences in order to accommodateshrinkage or stretching of the strand as it passes between the rollsshould this be desired. When the strand is wound along the circumferenceof a single-tapered porous roll, shrinkage or stretching of the strandoptionally may be carried out depending upon whether the strandinitially contacts the porous-tapered roll at its wide end or its narrowend respectively, and whether the particular strand has a propensity toshrink or to stretch at the temperature of the gas being expelled.

The gas expelled through the surface of the porous roll when conductingthe present process may be raised to the desired elevated temperature byany convenient means. In a preferred embodiment of the invention the gaspasses over one or more electric-resistance heating units positionedwithin the interior of each porous roll.

The strand of stabilized fibrous material produced in the presentprocess may optionally next be carbonized or carbonized and graphitizedat more highly elevated temperatures in a nonoxidizing or inertatmosphere, according to techniques known in the art. During thecarbonization reaction elements present in the strand of stabilizedmaterial other than carbon, e. g., nitrogen, hydrogen and oxygen, aresubstantially expelled. The term carbonized" as used herein is definedto describe a product consisting of at least about 90 percent carbon byweight. Suitable atmospheres include nitrogen, argon, helium, etc. Aparticularly preferred carbonization or carbonization and graphitizationprocess is disclosed in commonly assigned U.S. Ser. No. 777,275, filedNov. 28, 1968 of Charles M. Clarke which is herein incorporated byreference.

The following examples are given as specific illustrations of theinventions. It should be understood, however, that the in vention is notlimited to the specific details set forth in the examples.

EXAMPLE I An acrylonitrile homopolymer is dry spun to produce a 40 filcontinuous yarn, and is hot drawn at a draw ratio of about 7.5:] toobtain a highly oriented fibrous material having a single filamenttenacity of about 7 grams per denier. Twenty ends of this yarn are thenplied to produce the 800 fil strand having a total denier of about 1,150which is utilized as the starting material.

As shown in H6. 1, the strand of acrylic fibrous material may beprovided on a bobbin 4 located outside the substantially enclosedtreatment chamber 6 having walls 8. Situated within the heat treatmentchamber 6 is provided a cantilevered rotatable roll 10 having theconfiguration of a truncated cone and a porous surface. The wide end 12of the roll has a diameter inches, and the narrow end 14 of the roll hasa diameter of 4.5 inches. The length of the roll is 24 inches. Therotatable roll 10 is mounted upon a hollow conductive shaft 16 whichextends through a seal in the wall of the heat treatment chamber 6, andis driven by the aid of pinion l8 and worm gear 20. The hollowconductive shaft is bolted to supporting member 21 with the aid of fixedend plate 22 and is rendered rotatable by bearing 24.

Air is continuously supplied at an adjustable overpressure to the end 28of the hollow conductive shaft 16 which extends through supportingmember 21 by a fan (not shown). A multilead cable 30 extends into hollowshaft 16 and supplies electrical current to resistance heaters (notshown) situated within rotatable roll 10. Air introduced into hollowshaft 16 at end 28 passes over resistance heaters and is continuouslyexpelled outwardly through the porous surface 32 of rotatable roll 10.

As shown in FIG. 2, the hollow conductive shaft of conduit 16 iscoextensive with the length of rotatable roll 10 and further extendsthrough seal 34 in the opposite wall of the heat treatment chamber 6where it is capped. Such extension of hollow conductive shaft 16 throughthe wall of the chamber lends additional support to the rotatable roll10. Nonconductive end plates 36 and 38 are situated at the wide andnarrow ends respectively of rotatable roll 10. Additional dividers 40,42, 44 and 46 of a nonconductive material are positioned around thecircumference of central conduit 16 and define a series of heatingmodules 48, 50, S2, and 56 within the interior of rotatable roll 10. Theporous surface 32 of roll 10 is formed of a sintered ceramic materialthrough which air may be readily expelled outwardly. Situated withinheating modules 48, S0, 52, 54, and 56 are conductive screens 58, 60,62, 64, and 66 which are welded to pairs of conductive rings 68, 70, 72,74, and 76. One member of each pair of conductive rings is welded tohollow conductive shaft 16.

Multilead cable 30 includes a series of five individual leads 78, 80,82, 84, and 86 which pass through oversized openings in hollowconductive shaft 16 lined with insulative bushings 88, 90, 92, 94, and96. The individual power leads 78, 80, 82, 84, and 86 are welded to onemember of each pair of conductive rings 68, 70, 72, 74, and 76respectively. Electric current is supplied to each individual power lead78, 80, 82, 84, and 86 from a variable power source 98 with a slidingconnector or wiper arrangement 100 of the concentric ring type.

As the strand of acrylic fibrous material is unwound from bobbin 4 at arate of 2 meters/minute, it passes through an opening in the wall 8 ofthe heat treatment chamber 6 and meets the porous surface 32 of rotatingroll 10 at its wide end 12. The strand winds 11 turns per inch along theaxial length of rotating roll 10 in the absence of strand overlap.Electric current is supplied to individual leads 78, 80, 82, 84, and 86so that conductive screens 56, 60, 62, 64, and 6S impart a uniformtemperature of 270 C. to the air which is expelled outwardly through theporous surface 32 of roll 10. Such air penetrates the fibrousconfiguration of the strand wound upon roll 10 and stabilizes the same.The contact time of the strand upon roll 10 is 50 minutes. As shown inFIG. 1 the resulting stabilized strand is continuously unwound from thenarrow end 14 of rotating roll 10 and withdrawn from heat treatmentchamber 6 through opening 102 and wound upon bobbin 104.

Off gases from the stabilization treatment are removed from heattreatment chamber 10 through exhaust duct 106, with the aid of fan 108.If desired, gases removed from duct 106 may be scrubbed and at leastpartially recycled to the end 28 of hollow conductive shaft 16.

The resulting stabilized strand present upon bobbin 104 is black inappearance, exhibits a bound oxygen content of 8 percent by weight asdetermined by the Unterzaucher analysis, retains its original fibrousconfiguration essentially intact, and is nonburning when subjected to anordinary match flame.

The stabilized strand may be woven to form a fire-resistant fabric, orcarbonized or carbonized and graphitized in an inert atmosphere inaccordance with the teachings of US. Ser. No. 777,275, filed Nov. 20,1968 which is herein incorporated by reference. The carbonized orcarbonized and graphitized fibrous products find particular utility as areinforcing medium when suspended in a suitable matrix material to forman article useful as a strong lightweight structural component.

EXAMPLE ll Example 1 is repeated with the exception that the airexpelled outwardly through the porous surface 32 of roll 10 at heatingmodules 48, 50, S2, 54, and 56 is at 260 C., 275 C., 310 C., and 350 C.respectively. The fibrous strand penetrated by the heated air is passedcontinuously over each module for a residence time of approximately 5minutes. Substantially similar results are achieved.

EXAMPLE III The stabilization procedure of example 1 is repeated withthe exception that the strand of starting material is a 740 fil rayoncontinuous filament yarn having a total denier of about 2,200, the airexpelled outwardly through the surface 32 of roll 10 is maintained at auniform temperature of 220 C., and the strand is penetrated by theheated air while passing along the roll for a residence time of 60minutes.

The resulting strand retains its original fibrous configurationessentially intact, exhibits enhanced thermal stability, and is capableof undergoing carbonization.

EXAMPLE IV The stabilization procedure of example I is repeated with theexception that the strand of starting material is a 300 fil continuousfilament yarn of nylon 6T (condensation product of hexamethylenediamineand terephthalic acid) having total denier of about 900, the airexpelled outwardly through the surface 32 of roll 10 is maintained at auniform temperature of 3l5 C., and the strand is penetrated by theheated air while passing along the roll for a residence time of minutes.

The resulting stabilized strand retains its original fibrousconfiguration essentially intact, exhibits enhanced thermal stability,and is capable of undergoing carbonization.

EXAMPLE V The stabilization procedure of example I is repeated with theexception that the strand of starting material is a 400 fil continuousfilament yarn of poly-2,2'-m-5 ,5-bibenzimidazole (a preparation ofwhich is described in example ll of US. Pat. No. 3,174,497) having atotal denier of about 1,600 the air expelled outwardly through thesurface 32 of roll 10 is maintained at a uniform temperature of 470 C.,and the strand is penetrated by he heated air while passing along theroll for a resident time of minutes.

The resulting stabilized strand is nonburning when subjected to anordinary match flame and retains its original fibrous configurationessentially intact.

Although the invention has been described with preferred embodiments, itis to be understood that variations and modifications may be resorted toas will be apparent to those skilled in the art. Such variations andmodifications are to be considered within the purview and scope of theclaims appended hereto.

1 claim:

1. An apparatus for the continuous stabilization of a strand ofpolymeric fibrous material comprising a substantially enclosed heattreatment chamber, means for continuously introducing a strand offibrous material into said heat treatment chamber, means forcontinuously withdrawing a strand of fibrous material from said heattreatment chamber, at least one rotatable roll situated within saidchamber having a porous surface, drive means capable or rotating saidroll, conduit means essentially coextensive with the length of said rollin a communicative relationship to said porous surface of said roll,heating means situated within said rotatable roll, and means forsupplying a gas to said conduit means.

2. An apparatus according to claim 1 wherein said rotatable roll havinga porous surface has a tapered configuration.

3. Apparatus according to claim 1 wherein said rotatable roll having aporous surface has an essentially uniform cylindrical configuration, andsaid apparatus is additionally provided with a rotatable skewed roll ina paired relationship to said rotatable roll.

4, An apparatus according to claim 1 wherein means are provided forsupplying said gas at successively elevated temperatures along saidrotatable roll.

5. An apparatus for the continuous stabilization of a strand ofpolymeric fibrous material comprising a substantially enclosed heattreatment chamber, means for continuously introducing a strand offibrous material into said heat treatment chamber, means forcontinuously withdrawing a strand of fibrous material from said heattreatment chamber, at least one rotatable roll situated within saidchamber having a porous surface, drive means capable of rotating saidroll, central conduit means essentially coextensive with the length ofsaid roll, dividing means positioned about the circumference of saidcentral conduit means capable of dividing means capable of dividing theinterior of said roll into a plurality of modules which communicate withthe porous surface of said roll and said central conduit means,resistance heating means situated within said modules, means forsupplying current to said resistance heating means, and means forsupplying cur rent to said resistance heating means, and means forsupplying a gas to said central conduit means.

6. An apparatus according to claim 5 wherein said rotatable roll havinga porous surface has a tapered configuration.

7. An apparatus according to claim 5 wherein said rotatable roll havinga porous surface has an essentially uniform cylindrical configuration,and said apparatus is additionally provided with a rotatable skewed rollin a paired relationship to said rotatable roll having a porous surface,

8. An apparatus according to claim 5 wherein said means for continuouslyintroducing a strand of fibrous material into said heat treatmentchamber is a bobbin.

9. An apparatus according to claim 5 wherein said means for continuouslywithdrawing a strand of fibrous material from said heat treatment zoneis a bobbin.

10. An apparatus according to claim 5 wherein exhaust means are providedto withdraw off gasses generated within said heat treatment chamber.

11. An apparatus according to claim 5 wherein said means for supplying agas to said central conduit means is a fan.

Patent No.

ICATE 6F CORR'E ,TIUIN $2223 l'ED S1 YIES. PATEr-I'r OFFICE CERT?3,632,092 Dated January 4, 1972 Inventofls) Dagobert E. Stuetz It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 8, line 73, delete "3,174,497" and insert -3,l74,947

Signed and sealed this 14th day of July 1972.

(SEAL) Attest:

ROBERT GO TISC HALK Commissioner of Patents EDWARD I LFLETCHER, JR.Attesting Officer

2. An apparatus according to claim 1 wherein said rotatable roll havinga porous surface has a tapered configuration.
 3. Apparatus according toclaim 1 wherein said rotatable roll having a porous surface has anessentially uniform cylindrical configuration, and said apparatus isadditionally provided with a rotatable skewed roll in a pairedrelationship to said rotatable roll.
 4. An apparatus according to claim1 wherein means are provided for supplying said gas at successivelyelevated temperatures along said rotatable roll.
 5. An apparatus for thecontinuous stabilization of a strand of polymeric fibrous materialcomprising a substantially enclosed heat treatment chamber, means forcontinuously introducing a strand of fibrous material into said heattreatment chamber, means for continuously withdrawing a strand offibrous material from said heat treatment chamber, at least onerotatable roll situated within said chamber having a porous surface,drive means capable of rotating said roll, central conduit meansessentially coextensive with the length of said roll, dividing meanspositioned about the circumference of said central conduit means capableof dividing means capable of dividing the interior of said roll into aplurality of modules which communicate with the porous surface of saidroll and said central conduit means, resistance heating means situatedwithin said modules, means for supplying current to said resistanceheating means, and means for supplying current to said resistanceheating means, and means for supplying a gas to said central conduitmeans.
 6. An apparatus according to claim 5 wherein said rotatable rollhaving a porous surface has a tapered configuration.
 7. An apparatusaccording to claim 5 wherein said rotatable roll having a porous surfacehas an essentially uniform cylindrical configuration, and said apparatusis additionally provided with a rotatable skewed roll in a pairedrelationship to said rotatable roll having a porous surface,
 8. Anapparatus according to claim 5 wherein said means for continuouslyintroducing a strand of fibrous material into said heat treatmentchamber is a bobbin.
 9. An apparatus according to claim 5 wherein saidmeans for continuously withdrawing a strand of fibrous material fromsaid heat treatment zone is a bobbin.
 10. An apparatus according toclaim 5 wherein exhaust means are provided to withdraw off gassesgenerated within said heat treatment chamber.
 11. An apparatus accordingto claim 5 wherein said means for supplying a gas to said centralconduit means is a fan.